Unit 6 - Solubility and Chemical Equilibrium

Question 0

What are some key properties of water?

Answer 0

• relatively high boiling point
• exists mostly at liquid state
• only nonmetallic substance that expands upon freezing
• very high heat capacity
• can dissolve variety of solutes

Question 1

What are some key roles water plays in biology?

Answer 1

• ion hydration, sodium and ion transport
• protein folding, activity and drug binding
• solubility, toxicity, and bioaccumulation

Question 2

What is hydrogen bonding such a strong intermolecular force in water?

Answer 2

• results from extreme dipole moment (polarity) in water

* water can form four hydrogen bonds (two with lone pairs and two with hydrogen atoms)

Question 3

What are solutes?

Answer 3

• molecules which dissolve in water

Question 4

What is hydration?

Answer 4

• solubilization of polar or ionic solutes

Question 5

What are ion-dipole interactions?

Answer 5

• when the negative dipoles of water are oriented toward cations (i.e. Na+) and the positive dipoles of water are oriented toward anions (i.e. Cl-)

Question 6

What happens when the strong dipole of water interacts with ions in solution or strong dipoles of other molecules?

Answer 6

• energy is released

Question 7

What is a hydration shell?

Answer 7

• formed when water molecules are coordinated around an ion

Question 8

How do we know if something will dissolve in water?

Answer 8

• salvation enthalpy is greater than lattice enthalpy

Question 9

What are electrolytes?

Answer 9

• solutes that produce ions that can act as carriers of electrical charge in a solution

Question 10

What determines the strength of an electrolyte?

Answer 10

• degree of ionization of electrolyte in aqueous solution
• stronger electrolytes result in higher currents
• strong: substance dissolves completely into ions in water
• weak: do not completely break apart into ions or do not break apart at all

Question 11

Why do higher positively or negatively charged salts tend to be insoluble?

Answer 11

• lattice enthalpies tend to be higher

Question 12

What can solubility rules help you determine?

Answer 12

• if solid will dissolve
• if salt is strong electrolyte or not
• if solid will form
• if reaction will occur between two salt solutions when mixed

Question 13

If two solubility guidelines conflict, what do you do?

Answer 13

• follow the lower-numbered guideline

Question 14

What are spectator ions?

Answer 14

• appear equally on both sides of a total ionic equation

* removed to get the net ionic equation

Question 15

What is the reaction quotient (Q)?

Answer 15

• ratio of product to reactant activities
• large: numerator is larger = more products
• small: denominator is larger = more reactants

Question 16

What are activities?

Answer 16

• effective concentrations of reactants or products in solution (or pressures for gases)

Question 17

How do you calculate reaction quotient (Q)?

Answer 17

Where reaction is: mA(aq) + nB(aq) –> xC(aq) + yD(aq)

The equation is: [aC]^x • [aD]^y / [aA]^m • [aB]^n

Question 18

What are solute activities?

Answer 18

• effective concentration of electrolytes in real or non-ideal solutions
• calculated by using γ [S] / [S]。(ratio of [solute]:[solute’s standard state ~1M] multiplied by its activity coefficient ~1)

Question 19

What are the assumed activity coefficients for solutes, gases, and pure solids or liquids

Answer 19

• solute: 1
• gas: 1
• pure solid or liquid: 1 (can ignore when setting up equilibrium constant)

Question 20

Why is it useful for activities to be unitless?

Answer 20

• solids, liquids, gases and aqueous solutions can be combined into one equilibrium expression

Question 21

What is the equilibrium value K?

Answer 21

• a specific Q value
• ratio of reactants and products at equilibrium
• tells us the extent to which a reaction proceeds and is independent of concentration
• large: farther right towards products
• small: farther left towards reactants
• dependent on temperature, pressure, and pH

Question 22

What is an equilibrium reaction?

Answer 22

• takes place in forward and backward directions simultaneously

Question 23

When does a reaction reach equilibrium or steady state?

Answer 23

• rate of forward and reverse reaction are equal

Question 24

What does it mean if Q is smaller than K?

Answer 24

• reaction will move in forward direction

Question 25

What does it mean if Q is equal to K?

Answer 25

• reaction does not move

Question 26

What does it mean if Q is larger than K?

Answer 26

• reaction will move in reverse direction

Question 27

Is breaking a bond endothermic or exothermic?

Answer 27

• endothermic (requires energy)

Question 28

How do you find the K value for the reverse reaction?

Answer 28

• take the inverse of the K value for the forward reaction

Question 29

What are five special types of equilibrium constants/K values?

Answer 29

• Ka: equilibrium dissociation of an acid
• Kb: equilibrium dissociation of a base
• Kw: autoionization of water
• Ksp: solubility product
• Kow: octanol/water partition coefficient

Question 30

What does Kow coefficient give a measure of?

Answer 30

• lipophilicity
• ratio of solute in octanol layer to solute in water layer
• larger value = more lipophilic and will remain in our bodies (fatty tissue) for longer (bioaccumulation)

Question 31

What is lipophilicity?

Answer 31

• fat-loving nature/non-polarity of a solute molecule

Question 32

What does Ksp give a measure of?

Answer 32

• solubility of salt in aqueous solution

* larger value = more soluble in water

Question 33

How can you determine if a precipitate will form?

Answer 33

• compare Q and Ksp values

* if Q > Ksp, a precipitate will form